N. fowleri is a facultative thermophile and is able to grow at temperatures up to 46 ☌ (115 ☏). This amoeba is able to grow best at moderately elevated temperatures making summer month infections more likely. N. fowleri is sensitive to drying and acid. Naegleria fowleri are excavates that inhabit soil and water. The transformation of flagellate to trophozoite occurs within a few hours. Once inside the nasal cavity, the flagellated form transforms into a trophozoite. The flagellate form does not exist in human tissue, but can exist in the cerebrospinal fluid. This biflagellate form occurs when trophozoites are exposed to a change in ionic concentration, such as placement in distilled water. This stage can be inhaled into the nasal cavity during swimming or diving. The flagellate is pear-shaped and biflagellate: this means that it has two flagella. In tissues, it appears they phagocytize (consume by enclosing and then digesting prey) red blood cells and destroy tissue by releasing cytolytic substances. In their free-living state, trophozoites feed on bacteria. The pseudopods form at different points along the cell, thus allowing the trophozoite to change directions. They travel by pseudopodia, which means that they extend parts of their body's cell membrane (the pseudopods) and then fill them with protoplasm to force locomotion. The trophozoites are characterized by a nucleus and a surrounding flexible membrane. This reproductive stage of the protozoan organism, which transforms near 25 ☌ (77 ☏) and grows best around 42 ☌ (106.7 ☏), proliferates by binary fission. The trophozoite attaches to the olfactory epithelium, where it follows the olfactory cell axon through the cribriform plate (in the nasal cavity) to the brain. The trophozoite is the infective stage for humans, when the organism can actively feed and divide. N. fowleri has been found to encyst at temperatures below 10 ☌ (50 ☏).
When conditions improve, the amoeba can escape through the pore, or ostiole, seen in the middle of the cyst. Factors that induce cyst formation include a lack of food, overcrowding, desiccation, accumulation of waste products, and cold temperatures. The cyst is a resilient, life-preserving capsule for the amoeba, that resists adverse conditions. The cyst is a spherical, single-layered, smooth wall about 7–15 µm in diameter, that encloses a single nucleus. Trophozoites change to cyst form to survive times when the environment is temporarily harsh. It does not form a cyst in solid human tissue, where only the amoeboid trophozoite stage exists, however the flagellate form has been found in cerebrospinal fluid. fowleri occurs in three forms – as a cyst, a trophozoite (ameboid), and a biflagellate. The amoeba was identified in the 1960s in Australia but appears to have evolved in the United States. As the water temperature rises, its numbers increase. It is found in warm and hot freshwater ponds, lakes and rivers, and in the very warm water of hot springs. Naegleria fowleri is a thermophilic, free-living amoeba. Biotic phases: cyst, trophozoite, flagellate
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